High-frequency oven



15, 1956 F. J. H. TIMMERMANS ETAL 3,

HIGH-FREQUENCY OVEN Filed Oct. 22, 19 3 Age/W United States Patent 3,235,702 HiGH-FREQUENCY OVEN Franciscus Josephus Hendricus Timmermans and Johan Posthuma Van Der Helm, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Oct. 22, 1963, Ser. No. 318,057 Claims priority, application Netherlands, Oct. 26, 1962, 284,802 13 Claims. (Cl. 219-1055) This invention relates to a high-frequency oven for heating an object by means of ultrahigh-frequency energy. More particularly, the oven comprises an ultrahigh-frequency generator for supplying high frequency oscillations to a folded wave-guide system in the form of a plurality of waveguide pieces located side by side and connected together, every two adjacent wave-guide pieces being separated from one another by a common boundary wall. The wave-guide system is provided with a channel for passage therethrough of the object to be heated in a direct-ion transverse to the common boundary walls of the wave-guide pieces located side by side. Each boundary wall has an aperture therein to permit passage of the object.

In high-frequency ovens of this type, special consideration must be given to the stray radiation which emerges from the high-frequency oven through the leadthrough channel. It the energy of the stray radiation that emerges is excessive, on the one hand the heating efiiciency is adversely affected and, on the other hand, injury is caused to the operators. Due to the stray radiation that emerges, such high-frequency ovens use only ultrahigh-frequency generators of comparatively low power for the high-frequency heating of objects for which only a narrow lead-through channel is required, for example, wire beds, foils and the like.

The present invention relates to a high-frequency oven of the kind mentioned in the preamble in which the possibilities of application are considerably extended in a very simple manner by making such high-frequency ovens suitable for ultrahigh-frequency generators of high output, if desired in combination with an increase in the dimensions of the lead-through channel. The height of the lead-through channel may be increased, for example, by a factor of 3, while simultaneously improving the over-all efliciency.

A feature of the high-frequency oven according to the invention is that its folded wave guide system is provided with a partition wall separating the wave-guide system for the ultrahigh-frequency oscillations into two separate portions. The ultrahigh-frequency generator is connected to incoupling apertures, locate-d one on each side of the partition wall, through an energy-coupling device which couples in the ultrahigh-frequency oscillations from the ultrahigh-frequency generator through the two incoupling apertures located on each side of the partition wall and without changing the propagation mode of the Wave.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 is a perspective view of one embodiment of a high-frequency oven according to the invention, and

ice

FIG. 2 is a cross-sectional view of the high-frequency oven shown in FIG. 1.

The high-frequency oven of FIG. 1 comprises a magnetron generator 1 which is designed for producing oscillations having a wavelength of, for example, 12 cm.

In the high frequency oven shown, the ultrahigh-frequency oscillations are supplied to a folded waveguide system, housed in a box 2, which has the shape of a plurality of waveguide pieces 3 located side by side and connected together, every two adjacent waveguide pieces 3 being separated from one another by a common boundary wall 4. In the device shown, ultrahigh-frequency oscillations of the TE mode are propagated through the folded waveguide system so that the electric field vector has a direction of polarisation transverse to the common boundary Walls.

In order to pass objects to be heated through the oven, the folded waveguide system 3 is provided with a leadthrough channel in a direction transverse to the boundary walls 4 of the juxtaposed waveguide pieces 3 which for this purpose each have a slotted lead-through aperture in a direction parallel to the boundary wall 4. The outlet aperature 5 of the lead-through channel is shown in FIG. 1 whereas the inlet aperture 5 (see FIG. 2) cannot be seen in this figure.

When an object 6 to be heated is thus moved through the lead-through channel, for example an object in the form of a band-shaped foil which is driven by driving rollers (not shown), the ultrahigh-frequencies of the TE mode are propagated through the sequential waveguide pieces 3 along the object 6 to be heated, resulting in this object being high-frequency heated in succession in the sequential waveguide pieces 3. Such high-frequency heating of the object is very effective, but a considerable amount of stray radiation occurs outside the high-frequency oven through the inlet and outlet apertures 5' and 5, respectively, of the lead-through channel. This stray radiation is responsible for the fact that heretofore magnetron generators 1 of low power only could be used in the high frequency oven.

In order that magnetron generators 1 of high power may be used in such a high-frequency oven in a very simple manner whilst reducing the scattered radiation, according to the invention the folded waveguide system 3 is provided with a partition wall 7 which divides the waveguide system 3 for the ultrahigh-frequency oscillations into two separate portions 8 and 9. The magnetron generator 1 is connected to incoupling aperatures 10 and 11, located one on each side of the partition wall 7, through an energy-coupling device which couples the ultrahigh-frequency oscillations from the magnetron generator 1, without change of the propagation mode of the wave, through the two incoupling apertures 10, 11 located in each side of the partition wall 7 into the folded waveguide system 3. In the embodiment shown, the energy-coupling device comprises a co-axial line 12 connected to the magnetron generator. The inner conductor 13 of the coaxial line extends in a direction transverse to the boundary walls 4 of the waveguide pieces 3 into a connecting waveguide 14 which surrounds the two incoupling apertures 10 and 11 located in each side on the partition wall 7. The partition wall furthermore comprises a division wall 15 which extends further from a point located between the inner conductor 13 of the coaxial line 12 and the coupling apertures 10 and 11 in the 3 partition wall 7. The connecting waveguide 14 extends in a direction away from the coupling slots 10 and 11 to a point beyond the co-axial inner conductor 13 for the purpose of positioning a short-circuit piston 16 therein which serves to match the load to the magnetron generator 1.

In the device shown, the ultrahigh-frequency oscillations originating from the magnetron generator 1 are coupled through the coaxial inner conductor 13 into the connecting waveguide 14 as an electromagnetic field of the TE mode with the electric field vector in a direction parallel to the co-axial inner conductor 13. The electromagnetic field thus coupled into the waveguide conductor 14 is supplied, after division by the division wall 15, through the incoupling apertures 10 and 11 on each side of the partition wall 7 as two separate electromagnetic fields of the TE mode. The high-frequency oscillations coupled by the co-axial inner conductor 13 into the connecting waveguide 14 are supplied as two separate electromagnetic fields one on each side of the partition wall 7 of the waveguide system 3 substantially without disturbing the TE mode of the wave so that energy losses, reflection phenomena and the like are substantially avoided. Each of the two said electromagnetic fields is led from the partition wall 7 in relatively opposite directions through the two separate portions 8, 9 of the waveguide system 3 towards the inlet and outlet apertures 5' and 5, respectively, of the lead-through channel. In order to further minimize any disturbance of the electromagnetic field during its supply on each side of the partition wall 7 in the waveguide system 3, it is advisable to provide a division wall 15 in the connecting waveguide 14 of a sufficient length. In the embodiment shown, this length is, for example, /2 \=6 cm.

When an object 6 to be heated is moved through the lead-through channel, high-frequency heating of the object by the electromagnetic field occurs in the sequential waveguide pieces 3. The electromagnetic field passes by the partition wall 7 and propagates on through the two parts 8 and 9 of the waveguide system 3, The two electromagnetic fields are thus considerably attenuated on their way from the partition wall 7 through the sequential waveguide pieces 3 to the inlet and outlet apertures 5 and 5 of the high-frequency oven. The strength of the electromagnetic field at the inlet and outlet apertures 5', 5 is no more than, for example, 10 to -20 db of the strength of the electromagnetic fields coupled in on each side of the partition wall 7. Therefore, the stray radiation emerging through the inlet and outlet apertures 5, 5 will undergo a corresponding additional attenuation. In the device shown, it is therefore possible to use magnetron generators of maximum output substantially without loss of energy and with reduced stray radiation. In the embodiment shown, for example, the magnetron generator 1 is designed for an output of 5 kilowatts.

In the device according to the invention, with further reduction in stray radiation, an improvement of the efficiency can also be achieved by matching the two energy portions supplied on each side of the partition wall 7 to the loads locally occurring. More particularly, this division of energy may be obtained in a simple manner by suitable positioning of the division wall in the connecting waveguide 14 and of the partition wall 7 in the waveguide system 3. If desired, for this purpose, the division Wall 15 may be arranged in the connecting waveguide 14 to be pivotable about a spindle located near the coupling slots 10, 11. In fact, more accurate matching of the load constituted by the object to be heated is thus obtained, which load usually has undergone a change in magnitude on its way through the high-frequency oven as a result of the heating process. The improved matching of the load means an increased absorption of energy in the object 6 to be heated, resulting in a reduction in the stray radiation and in improvement in efliciency.

With a load comprising glued foils, for example, an improvement in eificiency of 20% was obtained due to this step and a further reduction of the stray radiation by a factor of about 2.

For further illustration of the device according to the invention, FIG. 2 shows a cross-section of the high-frequency oven of FIG. 1. Data for a high-frequency oven which has been extensively tested in practice is given below:

Dimensions of high-frequency oven 2 40 60 9 cm. Section of waveguide pieces 8.6 2 cm. Dimensions of lead through slots 55 l cm. Dimensions of connecting waveguide 14 8.6 4.3 cm. Length of division wall 15 6 cm.

Aside from the improvement in the operation of the high-frequency oven because magnetron generators of very high output can be used without excess loss of energy and with an improvement in efficiency, the number of possible applications of this high-frequency oven are also considerably widened. In fact, by increasing the dimensions of the lead-through slots, the high-frequency oven can be made suitable for high-frequency heating of objects of other kind and size, for example, Pertinax plates having a thickness of 8 mm.

What is claimed is:

1. In a high-frequency oven for heating an object by ultra high-frequency energy including an ultrahigh-frequency generator for supplying ultrahigh frequency oscillations to a folded waveguide system comprising a plurality of Waveguide pieces located side by side and interconnected, every two adjacent waveguide pieces being separated from one another by a common boundary wall, and wherein the waveguide system is provided with a channel for passage therethrough of the object to be heated in a direction transverse to the common boundary walls of the juxtaposed waveguide pieces, each of said walls having a lead-through aperture, the improvement comprising a partition wall in the folded waveguide sysem of the high-frequency oven which divides the waveguide system for the ultrahigh-frequency oscillations into two separate portions, first and second incoupling apertures located one on each side of the partition wall, and energy-coupling means for coupling the ultrahigh-frequency oscillations from the ultrahigh-frequency generator, without variation of the kind of wave, to the two incoupling apertures located on each side of the partition wall.

2. A high-frequency oven as claimed in claim 1, wherein said energy-coupling means is arranged to couple an electromagnetic field of the TE mode into the waveguide pieces having its electric field vector in a direction transverse to the boundary walls of the waveguide pieces, characterized in that the energy coupling means comprises, a co-axial line which is connected to the ultrahigh-frequency generator, a connecting waveguide which surrounds the two incoupling apertures located on either side of the partition wall, the inner conductor of said co-axial line being connected to said connecting waveguide in a direction transverse to the boundary walls of the waveguide pieces, said connecting waveguide further comprising a division wall which extends from the incoupling apertures to a point located between the inner conductor of the co-axial line and the incoupling apertures in the partition wall.

3. A high-frequency oven as claimed in claim 2, characterized in that the length of the division wall is about half the wavelength of the ultrahigh-frequency oscillations produced.

4. A high-frequency oven as claimed in claim 2, characterized in that the connecting waveguide further extends in a direction away from the coupling apertures and beyond the co-axial inner conductor, and a shortcircuit piston positioned within said connecting waveguide at a point beyond said inner conductor for matching the load to the ultrahigh-frequency generator.

5. A high-frequency oven as claimed in claim 2, wherein said division wall in the connecting waveguide and said partition wall in the waveguide system are positioned so that the portions of energy supplied on each side of the partition wall are matched to the loads locally occurring.

6. A high-frequency oven as claimed in claim 2, further comprising means for pivotally mounting said division wall in the connecting waveguide about a spindle located near the incoupling apertures.

7. High frequency heating apparatus comprising a generator of high frequency energy and a waveguide system, said waveguide system comprising a plurality of wall portions defining an enclosure having an inlet and an outlet aperture for passage therethrough of an object to be heated, said waveguide system further comprising a plurality of spaced planar partition members within said enclosure extending transversely to the direction of passage of said object and defining a plurality of waveguide sections interconnected to form a serpentine path for said high frequency energy, each of said partition members having an aperture therein which together form a channel for passage therethrough of said object in a direction transverse to said partition members, a partition wall in said enclosure arranged to separate said enclosure into first and second separate waveguide portions for the flow of said high frequency energy, and means for supplying said high frequency energy to said first and second waveguide portions comprising first and second energy coupling apertures located on either side of said partition wall, said energy supply means further comprising means coupling said high frequency energy from said generator to said first and second energy coupling apertures.

8. High frequency heating apparatus comprising a generator of high frequency energy and a waveguide system, said waveguide system comprising a plurality of wall portions defining an enclosure and including opposed end walls having apertures therein for passage of an object to be heated, said enclosure further comprising two opposite side walls lying in planes parallel to the direction of passage of said object and a plurality of parallel spaced partition members within said enclosure extending transversely to the direction of passage of said object and interconnected to define a serpentine path for said high frequency energy, said partition members including substantially aligned apertures for passage of said object, a partition wall in said enclosure positioned intermediate said end walls and arranged to separate said enclosure into first and second separate Waveguide sections for the flow of said high frequency energy, said enclosure further comprising first and second energy coupling apertures located on either side of said partition wall for supplying said high frequency energy to said first and second waveguide sections, and waveguide means enclosing said first and second energy coupling apertures and coupling said high frequency generator to said first and second apertures.

9. Apparatus as described in claim 8 wherein said partition wall is located substantially midway between said end walls and said first and second energy coupling apertures are located in one of said side walls substantially midway between said end walls, said Waveguide means comprising a waveguide section extending transversely to said side walls and further comprising a division wall extending from said partition wall into said waveguide means for a distance of approximately one-half Wavelength of the high frequency energy generated by said high frequency generator.

10. Apparatus as described in claim 8 wherein alternate ones of said partition members extend from one of said side walls toward the other of said side walls in planes substantially perpendicular to said side walls and alternate other ones of said partition members extend from the other of said side walls toward said one side walls, and wherein said waveguide means comprises an adjustable division wall extending into said waveguide means from said first and second energy coupling apertures whereby the proportion of energy coupled from said high frequency generator into said first and second energy coupling apertures can be varied.

11. High frequency heating apparatus comprising an enclosed waveguide system including first and second opposed end walls having an inlet and an outlet aperture therein, respectively, for passage of an object to be heated through said enclosed waveguide system, said waveguide system further comprising two opposed side walls and a plurality of spaced partition members within said waveguide system which extend transversely to the direction of passage of said object and interconnected to define a serpentine path for said high frequency energy, each of said partition members including an aperture therein which together form a channel for passage of said object, a partition wall in said waveguide system positioned intermediate said end walls and arranged to separate said waveguide system into first and second separate waveguide sections in the direction of passage of said object, said waveguide system further comprising first and second energy coupling apertures located on either side of said partition wall for supplying high frequency energy to said first and second waveguide sections, source means external to said waveguide system for generating high frequency electromagnetic wave energy, and energy coupling means for supplying said wave energy to said first and second energy coupling apertures whereby said energy propagates through said first and second waveguide sections from said energy coupling apertures towards said inlet and outlet apertures, respectively.

12. Apparatus as described in claim 11 wherein said energy coupling means comprises a waveguide structure enclosing said first and second energy coupling apertures, and means positioned within said waveguide structure and adjacent said first and second energy coupling apertures for separating said high frequency energy into two separate portions.

13. Apparatus as described in claim 12 wherein said separating means comprises a single movable partition member for changing the ratio of energy of said two separate portions.

References Cited by the Examiner UNITED STATES PATENTS 2,560,903 7/1951 Stiefel 2l9-10.55

FOREIGN PATENTS 893,936 4/1962 Great Britain.

RICHARD M. WOOD, Primary Examiner. 

1. IN A HIGH-FREQUENCY OVEN FOR HEATING AN OBJECT BY ULTRA HIGH-FREQUENCY ENERGY INCLUDING AN ULTRAHIGH-FREQUENCY GENERATOR FOR SUPPLYING ULTRAHIGH FREQUENCY OSCILLATIONS TO A FOLDED WAVEGUIDE SYSTEM COMPRISING A PLURALITY OF WAVEGUIDE PIECES LOCATED SIDE BY SIDE AND INTERCONNECTED, EVERY TWO ADJACENT WAVEGUIDE PIECES BEING SEPARATED FROM ONE ANOTHER BY A COMMON BOUNDARY WALL, AND WHEREIN THE WAVEGUIDE SYSTEM IS PROVIDED WITH A CHANNEL FOR PASSAGE THERETHROUGH OF THE OBJECT TO THE HEATED IN A DIRECTION TRANSVERSE TO THE COMMON BOUNDARY WALLS OF THE JUXTAPOSED WAVEGUIDE PIECES, EACH OF SAID WALLS HAVING A LEAD-THROUGH APERTURE, THE IMPROVEMENT COMPRISING A PARTITION WALL IN THE FOLDED WAVEGUIDE SYSTEM OF THE HIGH-FREQUENCY OVEN WHICH DIVIDES THE WAVEGUIDE SYSTEM FOR THE ULTRAHIGH-FREQUENCY OSCILLATIONS INTO TWO SEPARATE PORTIONS, FIRST AND SECOND INCOUPLING APERTURES LOCATED ONE ON EACH SIDE OF THE PARTITION WALL, AND ENERGY-COUPLING MEANS FOR COUPLING THE ULTRAHIGH-FREQUENCY OSCILLATIONS FROM THE ULITRAHIGH-FREQUENCY GENERATOR, WITHOUT VARIATION OF THE KIND OF WAVE, TO THE TWO INCOUPLING APERTURES LOCATED ON EACH SIDE OF THE PARTITION WALL. 